package main

import (
	"fmt"
	"math/rand"
	"sync/atomic"
	"time"
)

type readOp struct {
	key  int
	resp chan int
}
type writeOp struct {
	key  int
	val  int
	resp chan bool
}

func main() {
	//As before we’ll count how many operations we perform.

	var readOps uint64
	var writeOps uint64
	//The reads and writes channels will be used by other goroutines to issue read and write requests, respectively.

	reads := make(chan *readOp)
	writes := make(chan *writeOp)
	//Here is the goroutine that owns the state, which is a map as in the previous example but now private to the stateful goroutine.
	// This goroutine repeatedly selects on the reads and writes channels, responding to requests as they arrive.
	// A response is executed by first performing the requested operation and then sending a value on the response channel resp
	// to indicate success (and the desired value in the case of reads).

	go func() {
		var state = make(map[int]int)
		for {
			select {
			case read := <-reads:
				read.resp <- state[read.key]
			case write := <-writes:
				state[write.key] = write.val
				write.resp <- true
			}
		}
	}()
	//This starts 100 goroutines to issue reads to the state-owning goroutine via the reads channel.
	// Each read requires constructing a readOp, sending it over the reads channel,
	// and the receiving the result over the provided resp channel.

	for r := 0; r < 100; r++ {
		go func() {
			for {
				read := &readOp{
					key:  rand.Intn(5),
					resp: make(chan int)}
				reads <- read
				<-read.resp
				atomic.AddUint64(&readOps, 1)
				time.Sleep(time.Millisecond)
			}
		}()
	}
	//We start 10 writes as well, using a similar approach.

	for w := 0; w < 10; w++ {
		go func() {
			for {
				write := &writeOp{
					key:  rand.Intn(5),
					val:  rand.Intn(100),
					resp: make(chan bool)}
				writes <- write
				<-write.resp
				atomic.AddUint64(&writeOps, 1)
				time.Sleep(time.Millisecond)
			}
		}()
	}
	//Let the goroutines work for a second.

	time.Sleep(time.Second)
	//Finally, capture and report the op counts.

	readOpsFinal := atomic.LoadUint64(&readOps)
	fmt.Println("readOps:", readOpsFinal)
	writeOpsFinal := atomic.LoadUint64(&writeOps)
	fmt.Println("writeOps:", writeOpsFinal)
}
